1. Field of the Invention
The present invention relates to a hydraulic cement composition having improved properties, which is prepared by incorporating an oligosaccharide which has been subjected to a special treatment into a hydraulic cement material such as a cement paste, mortar or concrete. More specifically, the invention relates to a hydraulic cement composition comprising a hydraulic cement material having blended therein, a modified oligosaccharide formed by treating the terminal aldehyde groups (reducing groups) of an oligosaccharide having a molecular weight in the oligo range by an appropriate method to convert those aldehyde groups to hydroxyl groups.
2. Description of the Prior Art
Hydraulic cement is very important as an ingredient of mortar, concrete and the like. Various cement additives have heretofore been investigated and commercially utilized for facilitating working of mortar and concrete and for improving the strength, water impermeability and other properties of concrete structures. Among the cement additives used for various purposes, water-reducing agents are most popular. When the amount of water added during mixing of mortar or concrete is reduced by using a water reducing agent, as is well known in the art, the strength of the hardened mortar or cement structure is remarkably improved.
As water reducing agents for cement, there have heretofore been used, for example, lignin sulfonates, gluconates, sodium naphthalenesulfonate-formaldehyde high molecular weight condensates and compositions comprising a polysaccharide, calcium chloride and triethanolamine.
Lignin sulfonates are recovered from the sulfite pulp-preparing process, but they are disadvantageous because a uniform water reducing effect cannot be expected, they have a hardening retarding effect and the amount of air incorporated in the cement cmposition is increased and this has a bad influence on the physical properties of the concrete or mortar. Gluconates exhibit a hardening retarding effect when incorporated in concrete in large amounts and hence, practical use of gluconates involves significant problems. When incorporated in concrete at high concentrations, sodium naphthalesulfonate-formaldehyde condensates have a high water reducing effect without any hardening retarding effect, but when they are incorporated at low concentrations, their water reducing effect is drastically lowered and generally is lower than the water reducing effect of the lignin sulfonates or gluconates.
As a polysaccharide type cement additive, there is known hydrolyzed starch having an average degree of polymerization of 3 to 25 (see Japanese Patent Publication No. 12436/67). However, when this additive is used alone, a hardening retarding effect beyond the permissible range is manifested and therefore, it is ordinarily used in combination with calcium chloride and a water-soluble amine. In the case of a reinforced concrete structure, however, calcium chloride has an adverse effect on prevention of rusting of the reinforcing iron rods and it promotes formation of rust when hardened cement is dried, shrunk or cracked. Moreover, the flexural strength is reduced by the incorporation of calcium chloride, although the compression strength is improved.
An additive which has a high water reducing effect when added at a low concentration and which also exhibits a reduced hardening retarding effect has been desired in the art, but there has not been developed a cement additive meeting both of these requirements to a sufficient degree.